The present invention relates to wiring boards with an electromagnetic shield, particularly wiring boards with an electromagnetic shield of easy grounding.
Wiring boards consisting of a plurality of parallel lines have been widely used as flat cables.
Reference 101 in FIG. 15 represents a conventional flat cable comprising a plurality of lines 112 longitudinally arranged in parallel on an elongate base film 111. Ten lines 112 are shown in this figure.
A cover film 113 is applied on lines 112 except both ends of lines 112, so that the part of each line 112 covered with cover film 113 forms a signal member 122 and both ends not covered with cover film 113 form pad members 121.
In order to electrically connect electric circuits using this flat cable 101, pad member 121 at one end of flat cable 101 is connected to one electric circuit and pad member 121 at the other end is connected to the other electric circuit.
Each line 112 consists of a copper foil having a thickness of several tens of micrometers, and line 112, base film 111 and cover film 113 are flexible so that flat cable 101 can be folded to connect electric circuits.
Flat cable 101 as described above has been used in various devices in recent years and raised the problem that flat cable 101 picks up noises.
If flat cable 101 were wholly covered with a metal foil, the metal foil could serve as an electromagnetic shield but a complex operation would be required for connecting the metal foil to lines at ground potential.
What is needed, therefore, is a flat cable having an electromagnetic shield that can be connected to ground wirings without any special operation.
An aspect of the present invention provides a wiring board comprising a wiring board body having a base film, a plurality of metal lines provided on the base film and a cover film provided on the side of the base film having the metal lines, and a first shield film and a second shield film provided on the side of the wiring board body having the cover film and the opposite side, respectively, wherein the cover film has an opening formed at a predetermined location above the metal lines so that the first shield film is connected to the metal line exposed under the opening, and the wiring board body has a through-hole penetrating at least the base film and the cover film so that the first and second shield films are connected to each other via the through-hole.
In an embodiment of the wiring board of the present invention, the through-hole also penetrates the metal line in addition to the cover film and the base film.
In an embodiment of the wiring board of the present invention, the through-hole and the opening at least partially overlap each other.
In an embodiment of the wiring board of the present invention, the through-hole is smaller than the opening and the through-hole is provided inside the opening.
In an embodiment of the wiring board of the present invention, the metal lines are provided on both sides of the base film.
In an embodiment of the wiring board of the present invention, the metal lines comprise a plurality of signal wirings and at least one ground wiring wider than the signal wirings and the opening is provided above the ground wiring.
In an embodiment of the wiring board of the present invention, the signal wirings have a narrow conductor part and a terminal part connected to each end of the narrow conductor part and wider than the narrow conductor part.
In an embodiment of the wiring board of the present invention, the ground wiring has a wide conductor part and a terminal part connected to each end of the wide conductor part and narrower than the wide conductor part.
In an embodiment of the wiring board of the present invention, the ground wiring has a wide conductor part and a terminal part connected to each end of the wide conductor part and narrower than the wide conductor part, and the terminal part of the signal wirings and the terminal part of the ground wiring have approximately the same width.
In an embodiment of the wiring board of the present invention, the through-hole penetrates the wide conductor part of the ground wiring.
Another aspect of the present invention provides a wiring board comprising a wiring board body having a base film, a plurality of metal lines provided on the base film and a cover film provided on the side of the base film having the metal lines, and a first shield film and a second shield film provided on the side of the wiring board body having the cover film and the opposite side, respectively, wherein the wiring board body has a through-hole provided at a predetermined location on the metal lines and penetrating the base film, the cover film and the metal line, and a metal film is formed on the inner circumferential face of the through-hole and connected to the metal line exposed on the inner circumferential face of the through-hole, and the first and second shield films are connected to each other via the through-hole and at least one shield film is connected to the metal film.
In the wiring board according to this aspect, the metal lines may be provided on both sides of the base film.
According to the present invention as defined above, the first shield film and the ground wiring are connected at the bottom of the opening provided in the cover film or within the hole provided in the cover film, and the first and second shield films are connected to each other via the hole.
Thus, the first and second shield films are connected to the ground wiring without any special member, whereby a wiring board with high reliability can be easily prepared.